Hydrocarbon solvent solutions of complexes of isopropyllithium and ethyllithium

ABSTRACT

Hydrocarbon, especially aliphatic and/or cycloaliphatic hydrocarbon, solvent solutions of complexes of isopropyllithium and ethyllithium, exemplified by (a) equimolar solutions of isopropyllithium and ethyllithium in n-hexane or cyclohexane, and (b) 25 mole % isopropyllithium and 75 mole % ethyllithium in n-hexane or cyclohexane. The hydrocarbon solvent solutions of said complexes, especially where said solvents are aliphatic or cycloaliphatic, have various advantages over conventionally used hydrocarbon solvent solutions of isopropyllithium as catalysts or initiators in polymerization reactions, telomerization reactions, metalation reactions, halogen-metal interchange reactions, and in the preparation of magnesium alkyls and other organometallics.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART

It has heretofore been known, as disclosed in J. American Chemical Society, Vol. 85, pp. 485-6 (Weiner and West, 1973), in the article entitled "Complex Formation Between Ethyllithium and t-Butyllithium", to produce complexes of ethyllithium and t-butyllithium by dissolving ethyllithium and t-butyllithium in benzene. This article points out that ethyllithium alone is sparingly soluble in cold benzene (generally speaking, ethyllithium has a solubility of 0.2 N in n-hexane and somewhat higher in cyclohexane at room temperature) but its solubility is greatly enhanced when the benzene solution contains t-butyllithium; and that the solution of the ethyllithium and the t-butyllithium forms a complex in which both the ethyl and t-butyl groups are bonded to lithium. The complexes are stated to be believed to be electron-deficient polymers of the type (EtLi)_(n) (t-BuLi)_(m-n), where m is a small number such as 4 or 6.

The said article further points out that, when benzene from a benzene solution of ethyllithium and t-butyllithium is evaporated, a low melting white solid residue is obtained which is highly soluble in pentane, unlike ethyllithium which is virtually insoluble in pentane; that the ratio of ethyl to t-butyl groups in the resublimed complex is nearly the same as in the original benzene solution; and that 1:1 ratios, as well as 1.8:1 ratios, of the ethyllithium to the t-butyllithium produced, on distillation, distilled products with ethyl: t-butyl ratios of 1.1:1 and 1.7:1, respectively, m.p. 68°-72° C. and 56°-59° C. Benzene solutions specifically containing 8 wt. % each of ethyllithium and t-butyllithium are disclosed in said article.

Finally, the aforesaid article states that it was not known whether the formation of mixed organolithium compounds will occur generally, but that preliminary results indicate that t-butyllithium enhances the solubility of phenyllithium in benzene, but only to a limited extent. No uses or utilities are disclosed or suggested for the complexes of the ethyllithium and t-butyllithium or the benzene or pentane solutions thereof; or, for that matter, of the very generally disclosed phenyllithium solutions in benzene to which t-butyllithium was added.

As is pointed out in the article by Weiner, Vogel and West entitled "The Physical Properties and Structure of t-Butyllithium", Inorganic Chemistry, Volume 1, No. 3, August, 1962, pure t-butyllithium is a colorless crystalline solid, readily soluble in hydrocarbon solvents. Solutions of pure t-butyllithium in refluxing n-heptane turn brown and deposit a precipitate after about an hour, indicating that noticeable decomposition occurs during this time. A comparison is referred to with ethyllithium in relation to the degree of association, and it is stated that the average degree of association of t-butyllithium is very nearly four over a considerable range of concentrations in solutions in benzene and n-hexane, whereas the average degree of association in benzene solutions for ethyllithium is about six.

It has also been known to the art to prepare complexes (a) of ethyllithium with polyisoprenyllithium, (b) of n-butyllithium with isoprenyllithium, (c) of sec-butyllithium and polyisoprenyllithium, and, generally, of corresponding complexes where polystyryllithium was used in place of polyisoprenyllithium, in liquid hydrocarbon solvents such as benzene and n-hexane, Macromolecules, Vol. 3, No. 3, May, June, 1970, pp. 333-337, article entitled "The Cross-Association of Polyisoprenyllithium with Ethyllithium", Morton, Patt and Fetters. These complexes have been prepared in connection with studies dealing with association phenomena in organolithium polymerizations in hydrocarbon solvents based upon the possibility of cross-association between the propagating polymer-lithium species and any residual alkyllithium initiator since this could lead to complex kinetics in both the initiation and propagation reactions. Such studies were based upon concentration solution viscosity measurements. The authors reach the conclusion that the following association equilibrium can be written for this system:

    (RM.sub.2 Li).sub.2 +(EtLi)⃡2RM;Li.(EtLi).sub.3

and that in the polymerization reaction preferential cross-association occurs.

Furthermore, it has been known, as disclosed in U.S. Pat. No. 3,452,111, patented June 24, 1969 on an application filed Dec. 9, 1966, which patent was issued to and is owned by the Assignee (now by change of name, etc., to Lithium Corporation of America, a Delaware corporation) of the present application, that the stability against decomposition of sec-butyllithium and other heat labile secondary alkyllithiums, notably those containing from 4 to 8 carbon atoms in the alkyl radicals, generally in the form of solutions thereof in inert organic solvents, can be substantially increased by the addition thereto of variable proportions specifically of isopropyllithium and/or n-butyllithium. This patent does not deal in any way with ethyllithium, makes no reference whatever to the enhancement of the solubility of ethyllithium in inert organic solvent solutions thereof by the addition thereto of sec-butyllithium (or, for that matter, by the addition thereto of n-butyllithium or of isopropyllithium), or to the enhancement of the stability of sec-butyllithium or n-butyllithium or isopropyllithium by the addition thereto or the admixture therewith of ethyllithium, and said patent never contemplated the discoveries to which the present invention is directed.

It has also heretofore long been known and disclosed in numerous patents in connection with the preparation of homopolymers as well as copolymers of butadienes such as 1,3-butadiene; isoprene; vinyl-substituted hydrocarbons; vinyl halides; vinylidene halides; esters of acrylic acid; esters of homologs of acrylic acid, and numerous other polymerizable monomers; as well as in the preparation of telomers, to utilize, as catalysts or initiators in such polymerization and telomerization reactions, metallic lithium; lithium hydrocarbons; alkyllithiums corresponding to the formula R(Li)_(x) where R is a saturated or unsaturated hydrocarbon radical selected from the group consisting of aliphatic, cycloaliphatic, aralkyl, alkaryl, and aromatic radicals, and x is an integer from 1 to 4, inclusive, and wherein the R group has a valence equal to the integer x and preferably contains from 1 to 20 carbon atoms. Examples thereof are methyllithium, ethyllithium, isopropyllithium, n-butyllithium, amyllithium, hexyllithium, t-octyllithium, cyclohexyllithium, s-butyllithium, t-butyllithium, and t-amyllithium, phenyllithium, tolyllithiums, xylyllithiums, alpha-and beta-naphthyllithiums, allyllithium, methallyllithium; hydrocarbon polylithium compounds such as methylene dilithium, ethylene dilithium, trimethylene dilithium, octadecamethylene dilithium, and 1,2-dilithium propane; polylithium aryl, aralkyl and alkaryl compounds such as 1,4-dilithium benzene, 1,5-dilithium naphthalene, 1,2-dilithium-1,3-diphenyl propane; tri and higher lithium hydrocarbons such as 1,3,5-trilithium pentane and 1,3,5-trilithium benzene.

The foregoing organolithium compounds are disclosed in, among other patents, U.S. Pat. Nos. 2,975,160; 3,065,218; 3,094,512; 3,231,635; 3,294,768; 3,297,793; 3,301,840; 3,317,918; 3,324,191; 3,332,856; 3,427,364; 3,449,306; 3,464,961; 3,465,065; 3,498,960; 3,513,056; 3,554,911; 3,558,575; 3,607,846; 3,652,516; 3,692,874; 3,742,077; 3,752,501; 3,760,025; 3,787,377; 3,840,616; 4,057,601; 4,076,914; and 4,237,245; Canadian Patent No. 750,006; and Australian Patent No. 262,782. The general statement is made in some of these patents, after listing many of the aforesaid organolithium compounds, including unsaturated organolithium compounds and aryl, aralkyl and alkaryl lithium compounds such as allyllithium, methallyllithium, phenyllithium, tolyllithiums, xylyllithiums and naphthyllithiums, that mixtures of such organolithium compounds can be used, but no particular examples of any such mixtures are given. Illustrative of such patents are U.S. Pat. Nos. 3,506,631 and 3,632,563; and British Pat. Nos. 817,693; 817,695; and 994,726. None of these patents provides any concept or teachings which would lead one versed in the art to my present invention and the important benefits which result therefrom.

With due regard for the foregoing disclosures in the above-enumerated patents concerning the uses, as catalysts or initiators, of any of large numbers of different organolithium compounds in polymerization and other reactions, or, as noted above, very generally stated mixtures of such organolithium compounds, it will be seen from said patents that, in practically all of them, in the actual disclosed working examples, with very minor exceptions, n-butyllithium is the catalyst or initiator of choice. This is because it has been found to be, with very limited exceptions, the most desirable organolithium compound from the overall standpoints of its effectiveness utility-wise for the intended reactions, its relative ease of handling, manufacture and for other reasons as well.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

In connection with considerable investigatory work which I have conducted and have had conducted, it has been found that the behavior and properties of mixed alkyllithiums in hydrocarbon solvents, for instance, aliphatic or cycloaliphatic liquid hydrocarbon solvents, is unpredictable. Thus, in the case of methyllithium, I have found that, for instance, whereas the complexes of isopropyllithium with ethyllithium of the present invention can highly effectively be prepared by the methods described below in the illustrative general procedure and working Examples of this specification, such procedures and methods are ineffective or essentially or practically inoperative for the preparation of complexes of isopropyllithium and methyllithium, or complexes of t-butyllithium and methyllithium or complexes of n-butyllithium and methyllithium or complexes of sec-butyllithium and methyllithium, nor by the mixing of independently-prepared isopropyllithium, t-butyllithium or n-butyllithium or sec-butyllithium with independently-prepared methyllithium in liquid hydrocarbon solvents illustrative of which are n-hexane or cyclohexane.

I have discovered, among other things, that isopropyllithium forms complexes with ethyllithium which have important advantages over isopropyllithium alone or ethyllithium alone, or over solutions thereof in liquid hydrocarbon solvents, particularly aliphatic and/or cycloaliphatic hydrocarbon solvents, such as hexane or cyclohexane, as well as in their usefulness as catalysts or initiators in polymerization and other reactions. I have discovered that the addition of isopropyllithium results in materially increasing the solubility of ethyllithium in said solvents, exemplified particularly by hexane and cyclohexane. I have further discovered that, for instance, under certain conditions and circumstances, the complexes which result from such mixtures of isopropyllithium and ethyllithium, when dissolved in hydrocarbon solvents, notably n-hexane and/or cyclohexane, are more thermally stable than isopropyllithium, depending, in certain cases, on the mole ratios of the isopropyllithium to the ethyllithium, and also depending on the concentrations of the complexes of the isopropyllithium and ethyllithium and also being, to some extent, in certain instances, influenced by the particular hydrocarbon solvents in which said novel complexes are dissolved. Such thermal stability tests have been carried out at a temperature of 40° C. and for time periods in excess of 100 days. In the case of complexes of 25 mole % isopropyllithium and 75 mole % ethyllithium in dilute solutions in n-hexane or cyclohexane, tests show a thermal stability about double that of isopropyllithium. In the case of complexes of equimolar proportions of isopropyllithium and ethyllithium, the thermal stability was of about the same order as that of isopropyllithium alone.

In general, the stability of the complexes of isopropyllithium and ethyllithium tend to be greater, at various temperatures, illustratively at about 40° C., when such complexes are in the form of dilute solutions in liquid hydrocarbon solvents, illustratively, hexane or cyclohexane or mixtures thereof. Such dilute solutions may vary in their content of said complexes but, generally speaking, it is advantageous to market them in the form of solutions containing from about 12 to about 25 wt. %, or from about 12to about 40 wt. % of said complexes, particularly about 15 to about 25 wt. %. Thus, by way of illustration, as has been indicated above, dilute solutions of complexes of 25 mole % isopropyllithium and 75 mole % ethyllithium, in solution in cyclohexane, stored at 40° C. over a period of 37 days, showed an RLi loss per day of 0.164%; whereas a complex comprising equimolar proportions of isopropyllithium and ethyllithium showed an RLi loss per day, stored at 40° C. over a period of 42 days, of 0.25%.

In this same vein, concentrated solutions, considered as containing at least 40 wt. % of the complexes, and more commonly those containing from about 60 to 65 weight % of the complexes, depending upon the solubility of the particular complexes in given hydrocarbon solvents, while still maintaining substantial clarity of the solutions of said complexes, tend to be less stable than dilute solutions. The solubility of the complexes is generally dependent upon the mole percentages of the isopropyllithium and ethyllithium of the particular complex and, as indicated above, upon the particular hydrocarbon solvent used. Where a complex of equimolar proportions by weight of the isopropyllithium and ethyllithium is initially prepared containing, say, 15 or 25 or under 40 wt. % of said complex dissolved in hexane or cyclohexane, such can be concentrated by evaporating off hexane to such an extent that the resulting concentrate contains about 73 wt. %, more or less, for instance, from about 40 to about 73 wt % of the complexes of said complex in the form of a clear solution.

As indicated above, thermal stability tests have been previously carried out on liquid hydrocarbon solutions of different concentrations of isopropyllithium alone, at the illustrative temperature of 43° C. Furthermore, although, as previously stated, ethyllithium is very sparingly soluble in such liquid hydrocarbons as hexane and cyclohexane, thermal stability tests were conducted on a comparatively dilute, yet saturated, solution (about 0.4 N) of ethyllithium in cyclohexane, as noted below. So far as I am aware, prior to my present invention, no thermal stability data have been reported in the previous literature in regard to ethyllithium in solution. A knowledge of its thermal stability properties is important because the complexes of the present invention generally, and especially advantageously, contain at least about 50 mole % of ethyllithium. Prior to my present invention, ethyllithium, while per se being well known to the art, had essentially no commercial value because, apart from other considerations, of its very low solubility in liquid hydrocarbon solvents, as well as a relatively minimal knowledge concerning the scope of other alkyllithiums substantially to enhance its solubility in liquid hydrocarbon solvents, and a lack of knowledge by the prior art of the effect on the thermal stability of the complexes which might be formed between ethyllithium and other particular alkyllithiums.

The following Tables I and II disclose tests run in regard to the thermal stability of complexes of equimolar proportions of isopropyllithium and ethyllithium (denoted in Table I as IPEL 1:1); and complexes of 25 mole % isopropyllithium and 75 mole % ethyllithium (denoted in Table II as IPEL 25:75) each in wt. % proportions of ˜5% in cyclohexane.

                  TABLE I                                                          ______________________________________                                         THERMAL STABILITY OF IPEL 1:1 IN CYCLOHEXANE                                   40° C. Storage                                                                 Total                 Loss of                                           Days   Base (N)     V.sub.2 O.sub.5 (N)                                                                     Active RLi (%)                                    ______________________________________                                          0.sup.(1)                                                                            0.93         0.85     0                                                  7     0.93         0.85     0                                                 21     0.91         0.79     7.0                                               28     0.89         0.76     10.5                                              35.sup.(2)                                                                            0.89         0.74     12.9                                              42     0.89         0.76     10.5                                              ______________________________________                                          .sup.(1) Sample clear containing no precipitate.                               .sup.(2) Sample turbid containing a precipitate.                         

                  TABLE II                                                         ______________________________________                                         THERMAL STABILITY OF IPEL                                                      25:75 IN CYCLOHEXANE                                                           40° C. Storage                                                                 Total                 Loss of                                           Days   Base (N)     V.sub.2 O.sub.5 (N)                                                                     Active RLi (%)                                    ______________________________________                                          0.sup.(1)                                                                            0.93         0.82     0                                                  9     0.94         0.83     0                                                 16     0.92         0.79     3.6                                               23     0.91         0.78     4.8                                               30.sup.(2)                                                                            0.88         0.78     4.8                                               37     0.88         0.77     6.1                                               51     0.88         0.74     9.7                                               65.sup.(2)                                                                            0.88         0.70     14.6                                              ______________________________________                                          .sup.(1) Sample clear containing no precipitate.                               .sup.(2) Sample hazy containing a small amount of precipitate.           

                  TABLE III                                                        ______________________________________                                         Thermal Stability of                                                           ethyllithium in Cyclohexane                                                    at 40° C.                                                                      Total                 Loss of                                           Days   Base (N)     V.sub.2 O.sub.5 (N)                                                                     Active RLi (%)                                    ______________________________________                                          0.sup.(1)                                                                            0.44         0.41     0                                                 22     0.41         0.40     2.4                                               64     0.44         0.41     0                                                 114    N.A.         0.39     4.9                                               ______________________________________                                          .sup.(1) Sample clear.                                                   

I have also found that complexes of equimolar amounts of isopropyllithium and ethyllithium in various hydrocarbon solvents as, for example, n-hexane or cyclohexane, can be concentrated by careful evaporation to produce clear concentrates of said complexes (containing about 73 wt. % in n-hexane and 67 wt. % in cyclohexane) with no precipitation. Preparation of such isopropyllithium and ethyllithium complexes, in the form of clear solutions in said solvents, containing higher mole percentages of ethyllithium indicated that 1 isopropyllithium is needed to solubilize 5 ethyllithium (hexamer). The concentrations of these solutions were about 1.0 N. Attempts to incorporate more ethyllithium result in an insoluble product left on the filter. When ethyllithium is also prepared directly from ethyl chloride and a lithium dispersion, the resultant ethyllithium crystals can be dissolved and complexed with isopropyllithium in the same ratio (isopropyllithium/5 ethyllithium) as described above.

The relative proportions of the isopropyllithium and the ethyllithium are variable. The ratio of the isopropyllithium to the ethyllithium will generally, on a mole basis, be from about 1:9 to about 9:1. The extent of the solubility limits of said complexes, while maintaining clarity of the solution, will depend upon the particular isopropyllithium-ethyllithium complex, the particular hydrocarbon solvent, and the particular temperature of the solvent. Thus, for example, equimolar amounts of isopropyllithium and ethyllithium are highly soluble in n-hexane and in cyclohexane. Relative mole proportions of 25% isopropyllithium and 75% ethyllithium are soluble to an extent to produce a somewhat lower wt. % in n-hexane and in cyclohexane. In general, it is advantageous to utilize mixtures of isopropyllithium and ethyllithium, in solutions of the aforesaid hydrocarbon solvents, in which the mole ratio of the isopropyllithium to the ethyllithium is 1:1, or 35:65 or 25:75. Equimolar proportions of isopropyllithium and ethyllithium can produce clear solutions containing as high as about 73 wt. % of such complex at room temperature in n-hexane if one desires such highly-concentrated solutions; while, in cyclohexane, clear solutions can be obtained in wt. concentrations of the same complex as high as approximately 67 wt. % at room temperature.

As indicated above, the complexes of the isopropyllithium and the ethyllithium, particularly in solution in aliphatic and/or cycloaliphatic hydrocarbon solvents, are highly useful, and at substantial economical advantages, as has been indicated above, in various reactions where isopropyllithium and where n-butyllithium solutions in such solvents have been used, such as initiator/catalysts for stereospecific polymerization of conjugated dienes, such as butadiene and isoprene, and for copolymerization of dienes with vinyl aromatic compounds such as styrene, such as are disclosed in the patents listed above; as well as for use as cocatalysts for low pressure (Ziegler) polymerization of α-olefins; as well as in other reactions such as metalation reactions in which hydrogen is replaced by lithium; in halogen-metal interchange reactions; metalation of substrates to form carbanion intermediates; and in the preparation of magnesium alkyls such as are disclosed in U.S. Pat. Nos. 3,646,231 and 3,755,478.

While n-hexane and cyclohexane represent the liquid hydrocarbon, particularly the aliphatic and cycloaliphatic hydrocarbon, solvents of choice in which the complexes of isopropyllithium and ethyllithium of the present invention are used, and are prepared for use, various other inert aliphatic or aromatic hydrocarbon solvents or mixtures thereof which can be used, although generally less preferred, which will usually contain from 5 to 12 carbon atoms, are n-pentane, 2,4-dimethylhexane, octane, isooctane, n-decane, dodecane, methylcyclohexane, benzene, toluene, n-propyl benzene, isopropylbenzene, xylenes, and the like. Mixtures of such liquid hydrocarbons can be employed as, for example, mixtures of n-hexane and cyclohexane in variable proportions to each other such as 50-50 mixtures, 75-25 mixtures, 60-40 mixtures, etc. Generally speaking, however, it is more desirable to use a single liquid hydrocarbon solvent since no particular advantage is generally achieved by using mixtures thereof.

From a manufacturing point of view, the isopropyllithium/ethyllithium complexes, dissolved in aliphatic and/or cycloaliphatic hydrocarbon solvents, have the further advantage over isopropyllithium by reason of the fact that they possess an overall lower molecular weight than isopropyllithium which results in increasing the capacity of an installation since the capacity of any installation increases inversely proportionally to the molecular weight of the mixture constituting the isopropyllithium/ethyllithium complex contrastingly to the higher molecular weight of the isopropyllithium.

In the preparation of the complexes of isopropyllithium and ethyllithium in accordance with my present invention, it has been found to be especially satisfactory to prepare them directly by reacting a premixture of isopropyl chloride or bromide and ethyl chloride or bromide, most desirably in the form of a relatively homogeneous premixture, with a stirred dispersion or slurry of finely divided lithium metal in a liquid hydrocarbon, particularly of aliphatic or cycloaliphatic character, such as n-hexane or cyclohexane, in which the complexes produced are soluble, said reaction being advantageously carried out at a temperature in the range of about 25° to about 35° C. It is particularly desirable that the reaction be initiated by initially adding to the stirred lithium metal dispersion or slurry a small amount, usually not more than about what is equivalent to about 2% of the total of the premixture of the isopropyl chloride or bromide and the ethyl chloride or bromide, after which the said premixture is added gradually, under conditions of relatively vigorous stirring, until the reaction for producing said complexes is completed. The stirring is then discontinued and the unused or excess lithium metal is allowed to rise to the top of the reaction mass from where it is then drawn off. The "muds" which form during the reaction, consisting primarily or essentially of lithium chloride (or lithium bromide if isopropyl bromide and ethyl bromide are utilized), are separated from the liquid of the reacted mass, desirably by filtering, and said muds are washed one or more times with a given volume of the liquid hydrocarbon solvent, to recover from said muds the complexes adhering thereto or carried thereby. The washings may be added to the prior filtrate comprising the clear solution of the complexes in the liquid hydrocarbon solvent.

Alternatively, in the carrying out of the abovedescribed method, instead of allowing the lithium metal to rise to the surface and be drawn off after the completion of the reaction to produce the complexes and then separately separating the muds, as by filtration, the entire mass including the lithium metal and the muds are filtered off and separated from the filtrate comprising the solution of the complexes in the hydrocarbon solvent, and the separated solids are washed with the hydrocarbon solvent to recover the complexes carried by the separated solids.

As noted above, a homogeneous premixture of isopropyl chloride and ethyl chloride, in the selected predetermined proportions, is added to the lithium metal slurry in the carrying out of the reaction to produce the desired complexes of the isopropyllithium and ethyllithium. Instead of so proceeding, one may gradually feed simultaneously, separately, into the lithium metal slurry, the isopropyl chloride and the ethyl chloride, at rates so as to correspond to the desired selected predetermined proportions to produce the particular complexes of the isopropyllithium and ethyllithium. This approach, however, is distinctly less desirable and not preferred for a variety of reasons including handling difficulties as well as possessing other disadvantages.

No novelty is claimed per se in the preparation of the lithium metal dispersion proper in the hydrocarbon solvent. This is conveniently done by vigorous stirring or admixing finely divided lithium metal in an inert liquid medium, most desirably a mineral oil, illustratively a mineral oil such as that sold under the trade designation PRIMOL 155, or an admixture thereof with petrolatum, for instance, in proportions of about 25 to about 35 wt. % of the lithium metal, balance mineral oil or mineral oil admixed with some petrolatum. Mineral oil, alone, as the dispersing agent for the finely divided lithium metal is preferred. The lithium metal advantageously is admixed with or is made so as to contain a small percentage of sodium metal, e.g., 0.5 to 2%, preferably about 0.7% to about 1.7%, which serves to enhance the formation of the isopropyllithium and the ethyllithium complexes. To some extent, small proportions of other metals can be used in place of or in conjunction with sodium as, for example, potassium, rubidium, cesium or calcium, but sodium metal is especially useful. No novelty, however, is claimed per se broadly in using lithium metal admixed with a small proportion of sodium metal (and/or said other metals) in reactions with an alkyl halide to produce an alkyllithium since this is, in itself, known to the art. When reference is made to lithium metal in lithium metal dispersions, it will be understood to mean lithium metal containing or admixed with a small proportion, e.g., of the order of at least about 0.5% and up to about 2% more or less of sodium metal (and/or generally equivalent metal). The foregoing generally known procedural aspects are shown in various of the above-mentioned patents as well as in U.S. Pat. No. 3,452,112 of which I am one of the joint inventors. All operations, to the extent reasonably feasible, are carried out under inert gas conditions or in an inert gas atmosphere, such as argon or helium, since, as is well known to the art, air, oxygen and moisture are detrimental to reactions of the type disclosed in the present invention and the presence thereof is to be avoided to the maximum extent reasonably possible.

In the practice of the method of the present invention for the preparation of the novel complexes of isopropyllithium and ethyllithium, high yields of said complexes are commonly obtained, generally of the order of about 84 to about 95%. Thus, by utilizing the foregoing novel procedure, clear solutions of complexes of isopropyllithium and ethyllithium are directly formed in the particularly desired aliphatic or cycloaliphatic liquid hydrocarbon solvents, whereas, if the isopropyl chloride or bromide and the ethyl chloride or bromide are similarly reacted separately in the manner otherwise described, the aforesaid hydrocarbon-soluble isopropyllithium and the aforesaid hydrocarbon-insoluble ethyllithium, respectively, would be formed which is most unsatisfactory and would cause severe handling and manipulative problems.

Furthermore, by carrying out the production of the aforesaid isopropyllithium and ethyllithium complexes in the novel and advantageous manner described above, the additional important advantage is achieved of rendering unnecessary the use of strong Lewis Bases, e.g., ethers. In fact, and of definite significance, the simultaneously formed soluble species isopropyllithium apparently solubilizes the insoluble species ethyllithium as it forms thereby keeping the lithium metal surface clean and allows the reaction readily to proceed to completion, without complications. The preparation of the complexes of isopropyllithium and ethyllithium in accordance with the present invention has the still further advantage that, due to the lower molecular weight of said complexes, as compared to that of isopropyllithium, more C-Li equivalents/lb per batch is obtained which, as generally noted above, results in an increase of plant capacity per unit of time. In this connection, by way of more specific illustration, the increase of throughput or plant capacity, on a mole basis, for the production of an equimolar proportion complex of isopropyllithium and ethyllithium is about 49% greater than in the case of the production of isopropyllithium alone; and, in the production of a complex containing 25 mole % of isopropyllithium and 75 mole % of ethyllithium, said increase is about 62% greater than in the case of the production of isopropyllithium alone.

The following examples are illustrative of the preparation of the complexes of isopropyllithium and ethyllithium made in accordance with the present invention. An illustrative general procedure will first be described followed by specific examples. It will be understood that these examples are in no way limitative of my invention since various changes may be made in proportions of reactants and other ingredients, temperatures and times at which the reactions are carried out, and in other respects in light of the guiding principles and teachings disclosed herein. In said illustrative procedure and in said examples, the following described apparatus or equipment set-up was employed. It will, of course, be understood that this is simply exemplary and those skilled in the art can readily evolve modified apparatus set-ups particularly in connection with scale-up operations for large or commercial plant production of the complexes. All temperatures recited are in ° C.; and all percentages referred to are in terms of mole percentages unless otherwise expressly stated. For convenience, isopropyllithium will sometimes hereinafter be referred to as IPL; ethyllithium will be referred to as EL; and the complexes of isopropyllithium and ethyllithium will be referred to as IPEL.

Apparatus

500 ml round bottom reaction flask (3 neck)

Dry-ice condenser

250 ml jacketed dropping funnel (CO₂ -hexane cooled)

Thermometer (0° to 100° C.)

Mechanical stirrer

Cooling bath (CO₂ -hexane)

500 ml glass filter funnel (medium porosity)

500 ml round bottom receiving flask (3 neck)

Materials Used (except as specifically otherwise stated in the examples)

16.1 g Ethylchloride (EtCl) (0.25 moles)

19.6 g Isopropylchloride (IPCl) (0.25 moles)

26.0 g Lithium dispersion in petrolatum and Primol 155 (30 wt. %-1.1 g. atoms)

300 ml Cyclohexane (solvent)

100 ml Cyclohexane (dispersion wash)

5 ml n-Butyllithium (n-BuLi) in n-hexane (1.1% N-5.9 meq)-Li metal conditioner

Illustrative General Procedure

Preparation of IPEL from Premixed IPCl (or Br) and EtCl (or Br)

IPEL is prepared by reacting a premixture of IPCl and EtCl and a dispersion of finely divided lithium metal in a liquid hydrocarbon such as n-hexane or cyclohexane at a temperature of approximately 25 ° to approximately 35°. The chemistry is reflected by the following: ##STR1## A premixture of IPCl and EtCl, in predetermined molar proportions in relation to each other, as described above, is added to a vigorously stirred dispersion of finely divided metallic lithium in a hydrocarbon solvent under an inert gas atmosphere. To insure high yields of the IPEL, an excess of the lithium metal dispersion is used, for instance, of the order of about 10% to about 15%, said excess being based upon the excess stoichiometric amount of the lithium metal in relation to the premixture of the IPCl and EtCl. The lithium metal used in the dispersion contains, or is admixed with, as a part of the dispersion in a small amount, based on the weight of the lithium metal, of sodium metal, generally in the amount indicated above in the specification. Prior to the carrying out of the reaction to produce the IPEL, the lithium metal dispersion is conditioned or activated by stirring into the dispersion a small proportion of IPL or NBL or previously produced IPEL, which corresponds to about 1 mole % of the total charge of the premixture of the IPCl and EtCl, for a period of time which is variable but which may be of the order of about an hour. The exothermic alkylhalide-metal reaction is initiated at once by the addition of 2% of the total halide charge. On heat being noted, the remaining premixture of the IPCl and EtCl is added gradually or dropwise at a rate necessary to keep the reaction mass temperature preferably at about 30°. The reaction is highly exothermic and cooling is generally necessary. After reaction and, desirably, a postreaction period of time, of the variable order of a half hour or more, the IPEL solution is separated from the muds (LiCl and excess Li) by filtration and the muds are washed with the same solvent in which the complex was prepared. IPEL is analyzed by total base (LiOH) and vanadium pentoxide (active C-Li) assays. Recovered yields are determined by the following method: ##EQU1##

EXAMPLE 1

26 g of a finely divided lithium metal in petrolatum-Primol 155 and 100 ml dry cyclohexane are charged with the assembled and argon purged apparatus. The resulting slurry is stirred for 15 minutes and stirring is then stopped. The lithium is allowed to rise to the top of the solution. The 100 ml of cyclohexane wash containing the oil and petrolatum is then removed by syringe from the bottom of the flask. This is replaced by the reaction solvent (200 ml dry cyclohexane). The jacketed dropping funnel is cooled with the dry-ice n-hexane mixture. Then the 16.1 g of gaseous EtCl is condensed into the funnel. Next, the 19.6 g IPCL is added to the contents of the dropping funnel. The resulting mixture is shaken vigorously to insure complete mixing. The reaction is initiated by adding ˜1 ml of the mixed halides to the stirred lithium slurry. An immediate rise in temperature (3°) indicates spontaneous initiation. Addition of another 1 ml of the mixed halides solution brings the pot temperature to 33°. The dry-ice hexane cooling bath is then set in place. The IPCl-EtCl premixture is added dropwise over a period of about 98 minutes. The reaction is very sensitive to the chloride addition but is controlled easily by the cooling bath (αT=20°). The resultant reaction mass is slowly stirred overnight. Filtration of the final product and two 50 ml cyclohexane washes of the muds requires about 3 minutes. A volume of 345 ml of a clear, colorless solution of IPEL is recovered.

Analysis

Total Base=1.39 N

Active Alkyl (V₂ O₅)=1.33 N

Yield=95.9% (recovered)

The following additional examples, Table IV, show other runs made for the preparation of IPEL solutions in n-hexane and in cyclohexane using other mole ratios of IPCl-EtCl. Efficient removal of the intense heat of reaction all but eliminates the competing reaction of Wurtz coupling. The IPEL obtained from the above examples is crystal clear after filtration.

                                      TABLE IV                                     __________________________________________________________________________     Preparation of Isopropyllithium - Ethyllithium (IPEL)                                       Isopropyl-                                                        Isopropyl-   Ethyl Lithium Dispersion                                                                       Reaction                                                                               Metal    Analysis                         Ex.                                                                               Chloride                                                                             EtCl                                                                               (Mole gm   %    Solvent Conditioner.sup.(2)                                                                     Total                                                                               Active                                                                               Recovered             No.                                                                               (Moles)                                                                              (Moles)                                                                            Ratio)                                                                               (Atoms)                                                                             (Excess)                                                                            (Type)                                                                             (ml).sup.(1)                                                                       (Type)                                                                             (Moles)                                                                             Base (N)                                                                            Alkyl                                                                                Yield                 __________________________________________________________________________                                                              (%)                   2  0.25  0.25                                                                               1:1   1.1  10   Cyclo-                                                                             200 n-BuLi                                                                             0.005                                                                               1.39 1.33  95.9                                               hexane                                            3  0.25  0.25                                                                               50:50 1.1  10   Hexane                                                                             200 n-BuLi                                                                             0.005                                                                               1.34 1.23  84.4                  4  0.125 0.375                                                                              25:75 1.1  10   Cyclo-                                                                             200 n-BuLi                                                                             0.005                                                                               1.51 1.46  99.9                                               hexane                                            5  0.125 0.375                                                                              25:75 1.1  10   Hexane                                                                             200 Conc.                                                                              0.020                                                                               1.21 1.11  98                                                         BuLi                                      6  0.50  0.50                                                                               50:50 2.2  10   Cyclo-                                                                             400 Conc.                                                                              0.010                                                                               1.56 1.46  100                                                hexane  BuLi                                      7  0.05  0.45                                                                               1:9   1.1  10   Cyclo-                                                                             400 IPEL                                                                               0.005                                                                               0.85 0.82  92.5                                               hexane  50:50                                     __________________________________________________________________________      .sup.(1) Does not include the volume of solvent used for washing the           reaction muds. The wash generally is onehalf the volume used for the           reaction.                                                                      .sup.(2) The amount of RLi used to condition the lithium dispersion prior      to reaction.                                                             

With respect to the above-discussed thermal stability of the IPEL hydrocarbon solutions, a brief explanation as to the manner in which stability tests with respect thereto are carried out is believed to be in order. Because of the known readiness with which alkyllithiums degrade due to their high rate of reaction to O₂ and H₂ O with the resulting lowering of their C-Li activity, as well as causing other problems, it is desirable that such tests be carried out in a manner such as to minimize contact with O₂ and H₂ O and, thus, to obtain an accurate picture of the true thermal stability properties of said IPEL solutions. Thermal decomposition of alkyllithiums proceeds by lithium hydride elimination: ##STR2## The matter of thermal stability of alkyllithiums is highly important because the rate of thermal degradation dictates the way alkyllithiums must be handled, stored and shipped.

Thermal stability of alkyllithium is commonly carried out by placing samples thereof in rolled steel cylinders (30 and 55 in.³ volume). Prior to use, each cylinder is equipped with the appropriate fittings to insure a leak proof system and then is "pickled" or conditioned with the alkyllithium. The alkyllithium solution in the hydrocarbon solvent is then placed in the cylinder and analyzed for total base and active RLi (V₂ O₅ method). The sample is then placed in a constant temperature bath at 40° C. (±1° C.). Periodically, the cylinder is removed from the bath, opened and reanalyzed for total base and active RLi. From these data, the thermal stability of the alkyllithium is calculated and plotted on graph paper (% loss active RLi vs. time). Since the cylinder is opened and samples several times during the course of the test, the chance for atmospheric oxygen and H₂ O contamination is great. This can often result in erroneously high thermal stability data because the loss due to contamination is additive. In addition, lithium alkoxide formed by the reaction of O₂ with alkyllithium increases the rate of the thermal degradation of organolithium. A distinctly preferred method, whereby the contamination problem described above is at least largely circumvented, involves using several cylinders of the IPEL hydrocarbon solutions to be tested. In such preferred procedure, the tests are carried out as described above except that each cylinder is sampled only once. This procedure materially reduces the chance for atmospheric contamination, thus providing a more accurate thermal stability evaluation.

The following examples are illustrative of polymerization and metal-halogen exchange reactions which are effectively carried out by the utilization of complexes of isopropyllithium and ethyllithium in liquid hydrocarbon solutions made in accordance with the present invention.

The hydrocarbon solutions of the complexes of isopropyllithium and ethyllithium of the present invention can, in general, be used in place of solutions of n-butyllithium in known polymerization and copolymerization reactions to produce liquid as well as solid polymers and copolymers, oligomers, triblock polymers, "Star" polymers, metalation and other reactions. The following examples are illustrative of such usage. All temperatures cited are in °C.

EXAMPLE A

Preparation of Polystyrene.

To an oven-dried one pint sample bottle, purged with N₂, is added 150 ml of dry cyclohexane. The bottle is then capped with a septum. Using a syringe, 16.5 ml of freshly distilled styrene (inhibitor free) is added to the cyclohexane. Next, the reaction vessel is placed in a constant temperature bath at 36.5° C. and continously mixed using a shaker. 0.001 mole of the solution of the complex made in accordance with Example 1 is then added via syringe, followed by sealing of the septum with parafilm. A pale yellow color appears in a few seconds after said addition. The color of the solution becomes orange in approximately 30 seconds. The color intensity gradually increases with time and becomes a deep red after 12 hours. The polymerization is terminated after 24 hours with 2 ml of degassed isopropanol. A one ml sample of the resulting colorless solution is concentrated using a gentle N₂ purge. A resulting colorless film of polystyrene is obtained. The film of polystyrene is then subjected to GPC analysis for determination of M_(n), M_(w), M_(z), and corresponding molecular weight distributions. Based on the calculated MWD's of the polystyrenes obtained using the above procedure, the IPEL initiators produced a polydispersity of 1.1 to 1.3 compared to that of n-butyllithium which was 1.5. As a check for the procedure above, sec-butyllithium was also tested in the same manner. The MWD for sec-butyllithium is in agreement with existing data for this initiator.

EXAMPLE B

Metal-Halogen Exchange.

Under an argon atmosphere, 1 g of p-bromoanisole is dissolved in 50 ml of freshly distilled tetrahydrofuran and the solution is cooled to -78° C. One equivalent of the complex, which consisted of 50 mole % isopropyllithium and 50 mole % ethyllithium in hexane, is added over a 2 minute period with stirring. After 30 minutes, the reaction is quenched with 1 ml anhydrous methanol, followed by removal of the cooling bath. GC analysis of the resulting solution reveals that greater than 95% metal-halogen exchange had taken place. Also, any occurrence of alkylation could not be detected. High yields of exchange are also obtained when the above procedure is repeated using 3-bromothiophene and other arylbromides such as meta and ortho-bromoanisole, and o-bromo-α,α,α-trifluorotoluene. 

I claim:
 1. In a method of preparing liquid hydrocarbon solutions of complexes of isopropyllithium and ethyllithium in which the ratio of the isopropyllithium to the ethyllithium, on a mole basis, is from about 1:9 to about 9:1, the steps which comprise providing a stirred dispersion of finely divided lithium metal containing a small proportion of sodium metal in a liquid with which the lithium metal is essentially unreactive, discontinuing the stirring and allowing the lithium metal to rise to the top of the mixture, separating out the unreactive liquid and replacing it with a liquid hydrocarbon solvent, gradually adding to said lithium metal dispersion, under conditions of vigorous agitation and in an inert gas atmosphere, a relatively homogeneous mixture of (a) isopropyl chloride or bromide and (b) ethyl chloride or ethyl bromide in predetermined relative proportions to provide the aforesaid solutions containing the complexes in their above-stated mole ratios of the isopropyllithium and ethyllithium, and continuing the reaction at a temperature in the approximate range of about 20° to about 35°, under conditions of stirring, until said reaction is at least substantially completed, filtering and washing the reaction muds with a liquid hydrocarbon solvent for said complexes to produce a final clear hydrocarbon solution of said complexes.
 2. The method of claim 1, in which the mole ratio of the isopropyllithium to the ethyllithium in said complexes is equimolar.
 3. The method of claim 1, in which the mole ratio of the isopropyllithium to the ethyllithium is about 35 to about
 65. 4. The method of claim 1, in which the mole ratio of the isopropyllithium to the ethyllithium is about 25 to about
 75. 5. The method of claim 1, in which the hydrocarbon solvent is selected from the group of aliphatic and/or cycloaliphatic hydrocarbon solvents.
 6. The method of claim 1, in which the lithium content of said slurry is in excess of the stoichiometric amount thereof in relation to the amounts of isopropyl and ethyl chlorides or bromides.
 7. The method of claim 1, in which the weight percentage of said complexes in said aliphatic and/or cycloaliphatic hydrocarbon solvent is such as to produce a dilute solution thereof.
 8. The method of claim 7, in which said hydrocarbon solvent is selected from the group of n-hexane and/or cyclohexane.
 9. In a method of preparing liquid hydrocarbon solutions of complexes of isopropyllithium and ethyllithium in which the ratio of the isopropyllithium to the ethyllithium, on a mole basis, is from about 1:9 to about 9:1, the steps which comprise providing a stirred dispersion of finely divided lithium metal containing a small proportion of sodium metal in a liquid hydrocarbon selected from the group of aliphatic and cycloaliphatic hydrocarbons with which the lithium metal is essentially unreactive, gradually adding simultaneously to said lithium metal dispersion, under conditions of vigorous agitation and in an inert gas atmosphere, (a) isopropyl chloride or bromide and (b) ethyl chloride or bromide in predetermined relative proportions to provide the aforesaid solutions containing the complexes in their above-stated mole ratios of the isopropyllithium and ethyllithium, and continuing the reaction at a temperature in the approximate range of about 20° to about 35°, under conditions of stirring, until said reaction is at least substantially completed, and filtering to produce a solution of said complexes in said hydrocarbon solvent.
 10. In a method of preparing liquid aliphatic and/or cycloaliphatic hydrocarbon solutions of complexes of isopropyllithium and ethyllithium in which the ratio of the isopropyllithium to the ethyllithium, on a mole basis, is from about 1:9 to about 9:1, the steps which comprise providing a stirred dispersion of finely divided lithium metal containing a small proportion of sodium metal in a liquid with which the lithium metal is essentially unreactive, discontinuing the stirring and allowing the lithium metal to rise to the top of the mixture, separating out the unreactive liquid and replacing it with a liquid hydrocarbon solvent, gradually adding to said lithium metal dispersion, under conditions of vigorous agitation and in an inert gas atmosphere, a relatively homogeneous mixture of (a) isopropyl chloride or bromide, and (b) ethyl chloride or bromide in predetermined relative proportions to provide the aforesaid solutions containing the complexes in their above-stated mole ratios of the isopropyllithium and ethyllithium, and continuing the reaction at a temperature in the approximate range of about 20° to about 35°, under conditions of stirring, until said reaction is at least substantially completed, filtering and washing the reaction muds with a liquid hydrocarbon solvent for said complexes to produce a final clear hydrocarbon solution of said complexes.
 11. The method of claim 10, in which the lithium content of said slurry is in excess of the stoichiometric amount thereof in relation to the amounts of isopropyl and ethyl chlorides or bromides.
 12. The method of claim 11, in which the liquid hydrocarbon solvents are selected from the group of n-hexane and cyclohexane.
 13. The method of claim 11, in which the mole ratio of the isopropyllithium to the ethyllithium in said complexes is about equimolar.
 14. The method of claim 11, in which the mole ratio of the isopropyllithium to the ethyllithium is about 35 to about
 65. 15. The method of claim 11, in which the mole ratio of the isopropyllithium to the ethyllithium is about 25 to about
 75. 16. The method of claim 11, in which the mole ratios of the isopropyllithium to the ethyllithium in said complexes are selected from the group (a) about equimolar, (b) about 35 to about 65, and (c) about 25 to about 75, and in which the weight percentages of said complexes in said hydrocarbon solvent are such as to produce a dilute solution thereof.
 17. A composition comprising a clear solution in a liquid hydrocarbon solvent of a complex of isopropyllithium and ethyllithium in which the ratio, on a mole basis, of the isopropyllithium to the ethyllithium is in the range of about 1:9 to about 9:1.
 18. The composition of claim 17, in which the liquid hydrocarbon solvent is selected from the group of aliphatic and cycloaliphatic hydrocarbon solvents.
 19. The composition of claim 18, in which the mole ratio of the isopropyllithium to the ethyllithium in said complex is about equimolar.
 20. The composition of claim 18, in which the mole ratio of the isopropyllithium to the ethyllithium is about 12% to about 73%.
 21. The composition of claim 18, in which the mole ratio of the isopropyllithium to the ethyllithium is about 25% to about 75%.
 22. The composition of claim 18, in which the aliphatic or cycloaliphatic hydrocarbon is selected from the group of n-hexane and cyclohexane.
 23. The composition of claim 18, in which the weight percentage of said complex in said solution is in the range of about 12 to about
 25. 24. The composition of claim 23, in which the aliphatic or cycloaliphatic hydrocarbon is selected from the group of n-hexane and cyclohexane.
 25. The composition of claims 19, 20 or 21, in which the weight percentage in said solution is in the range of about 12 to about
 25. 26. The composition of claims 19, 20 or 21, in which the weight percentage of said complex in said solution is in the range of about 40 to about
 73. 